The quality of a chocolate is directly influenced by the geographic and genetic origin, and the conditions for treating the cocoa beans, from their cultivation in the field up to their processing in the factory. Once harvested, cocoa beans are thus subjected, in their country of origin, to a fermentation and a natural drying which are intended to cause the appearance of the flavor precursors. Unfortunately, the harvesting at maturity of the beans and the conditions for their fermentation are not always adequately controlled. Furthermore, the three principal types of cocoa trees of the species Theobroma cacao, called Criollo, Forastero and Trinitario, each produce beans having a different composition. Finally, the dried beans can also be damaged during their transport to the countries specialized in the processing of the beans. Industry must therefore address a wide variability in the composition of a batch of cocoa beans (see for example Smaffer M., The Manufacturing Confectioner, 92-94, June 1994).
The fermented and dried cocoa beans are then traditionally crushed to a greater or lesser extent, the outer coats are separated, and then they are subjected to roasting, combined where appropriate with alkalization, which are intended to cause the cocoa flavor and colour to appear. The roasting step involves Maillard reactions between the reducing sugars and the products of the degradation of proteins, especially the amino acids and the hydrolysis products (Wood and Lass, Cocoa, Longman Scientific & Technical, Longman Group UK, England, 1985, ISBN 0-582-46352-1).
The flavor precursors appear only during the natural fermentation of the beans, as a result of hydrolysis reactions. Experiments involving in vitro incubation of unfermented cocoa beans or bean fragments have thus shown that these hydrolysis reactions are dependent on the pH, the temperature and the compartmentation of the enzymes and of the substrates in the bean. Furthermore, the hydrolysis reactions are also sensitive to the presence of polyphenols. It is thus advantageous to extract the polyphenols from the beans using acetone, and also to incubate the said beans in acetic acid in order to decompartmentalize the enzymes and the substrates (Biehl B. et al., J. Sci. Food. Agric., 33, 1280-1290, 1982).
Furthermore, other studies have shown that cocoa beans comprise at least three protolytic activities involved in the appearance of the cocoa flavor precursors, namely an endoprotease having an optimum activity at pH 3.5, a carboxypeptidase having an optimum activity at pH 5.8, and an aminopeptidase having an optimum activity at pH 7. Experiments involving hydrolysis of purified cocoa bean globulin (protein having two bands of 31 kD and 47 kD on an SDS-PAGE chromatography gel), from which the polyphenols have been extracted, with commercial proteases and/or purified cocoa endoprotease and carboxypeptidase have shown that it was preferable to hydrolyse the globulin successively with cocoa endoprotease at pH 3.5, then with cocoa carboxypeptidase or a commercial carboxypeptidase at pH 5-6. In this way, a hydrolysis product and amino acid composition is obtained which is suitable for obtaining a cocoa flavor during subsequent roasting of the mixture in the presence of reducing sugars (Voigt J. et al., Food Chemistry, 50, 177-184, 1994).
Moreover, U.S. Pat. No. 2,965,490 describes a process for the in vitro hydrolysis of unfermented cocoa beans (green cocoa beans), intended to replace the natural fermentation of the beans. To this end, the green cocoa bean proteins are hydrolysed with acid or enzymatically, the carbohydrates in the said beans are hydrolysed enzymatically to produce simple sugars, and both hydrolysates are allowed to react under anhydrous conditions at a temperature and for a time sufficient to produce an aromatic factor. However, it should be stated that the polyphenols in the green seeds limit particularly the enzymatic hydrolysis of the storage proteins (see Comparative Example 1 below).
In the final analysis, the processes and studies described above are evidently intended to replace the natural fermentation of the cocoa beans with a controlled enzymatic hydrolysis of the green beans (problem caused by the polyphenols) or of their purified proteins (from which the polyphenols have been extracted). Furthermore, the quality and the quantity of flavor precursors necessary for the creation of a good cocoa flavor during roasting are not yet known.